Certain congenital conditions and acquired deformities related to surgery, irradiation, and/or trauma may result in varying sized and shaped voids in bone and soft tissue. For example, severe impacts to the head could leave the frontal, parietal and/or temporal areas of the craniofacial skeleton in need of repair. Cranial bone voids are commonly filled throughout the anterior, middle, and posterior cranial vaults, for example, using autologous bone flaps, standard or customized alloplastic implants, titanium mesh, biologic absorbable materials, tissue engineered substrates and/or liquid methyl methacrylate in order to provide much needed cerebral protection. However, in times where secondary cranioplasty requires a bone substitute, temporal hollowing needs to be corrected and/or prevented.
While cranial bone voids present via congenital deformities or traumatic injuries may be filled using any one or more of the above means to achieve structural soundness, replacement of soft tissue structures that overlie the bone void being filled and underlie adjacent skin tissue generally has to be accounted for in order to achieve a preferable cosmetic result. Bone flaps, standard or customized alloplastic implants, titanium mesh, and liquid methyl methacrylate that are used to fill bone voids do not account for soft tissue atrophy in the temporal area of the skull. Thus, these bone void filling means do not provide an adequate aesthetic reconstruction of this area. The main problems are that the temporalis muscle and temporal fat pad change shape, thickness and location following temporary skull bone removal, and therefore, when the cranioplasty with custom skull implant is required, one is often challenged by having to mobilize the scarred down muscle and fat from its abnormal, inferior position and then try to re-attach it to the outside of currently-designed, patient-specific craniofacial implants.
In many cases where bone is filled in the temporal region, the soft tissue loss in this area generally results in concavity referred to as temporal hollowing, as originally described in detail by the surgeon-inventor in 2015 [“Quantitative analysis of dual-purpose, patient-specific craniofacial implants for correction of temporal deformity. Operative Neurosurgery 11(2):205-12” and “Craniofacial reconstruction with poly (methyl methacrylate) customized cranial implants. Journal of Craniofacial Surgery 26(1):64-70.”) This deforming asymmetry reflects a deficiency in the bulk of the temporalis muscle or overlying temporal fat pad along the upper lateral face. Many patients who have undergone neurosurgical procedures that damage the integrity of the temporalis muscle during temporal or pterional craniotomy surgery in the temporal area are left with this concavity. Both aesthetic and reconstructive procedures that violate the temporal fat pad may also result in temporal hollowing. As such, the area of concern is a direct deformity related to a few etiologies such as temporalis muscle displacement or foreshortening from previous surgery, temporal fat pad atrophy, or soft tissue contraction from irradiation or aging. Thus, traditional implant methods require the surgeon to mobilize these scarred tissues off of the brain.
In patients with the common temporal hollowing, the top or cephalad part of the deformity is generally a concave depression due to the missing, above-mentioned etiologies. In addition, directly underneath and neighboring this concave depression is a convex bulge (directly cephalad to the zygomatic arch) that often originates from a displaced temporalis muscle. In some common instances, the temporalis muscle cannot be re-inserted since the bone flap is unable to be placed back into position, thereby leaving an absent fixation point adjacent the temporal crest. This not only accentuates the neighboring concave deformity above, it sometimes causes dynamic distortion during chewing since the temporalis muscle is involved with mastication.
Other reasons for the cephalad deficiency, or other head deformities, may entail temporal fat pad wasting, which is a defined layer of anatomical fat between the scalp and the skull which adds to the normal bulk of one's temporal region. It is often a sign of youthfulness. Many patients who have undergone neurosurgical and/or temporal procedures may lose the integrity of the temporalis muscle during temporal or pterional craniotomy surgery. Both aesthetic and reconstructive procedures that violate the temporal fat pad, such as coronal incisional approaches, for instance, may also result in temporal hollowing deformities, which can happen if a surgeon devascularizes the area with dissection or if the area has received irradiation or tissue resection for oncological treatment.
Numerous techniques have been described to augment the temporal area, including the placement of various standard or customized alloplastic implants, titanium mesh, free fat grafts, dermal grafts, tissue engineered substrates, the injection and onlay of various absorbable and permanent materials, loco-regional flaps, and, in some instances, free tissue transfer with microscopic technique. Temporal augmentation can restore the preoperative appearance of these patients; however, such augmentation is generally performed in a subsequent procedure after an initial procedure of filling a bone void in this area. Thus, these solutions are problematic because a revision surgery is generally required to correct the deformity, and the patient will likely exhibit aesthetic asymmetry prior to the revision surgery. There thus exists a need for a patient-specific cranial implant that provides both bony reconstruction and soft tissue reconstruction such that one or more revision surgeries will generally not be necessary. All previous implants follow the inferior, inward tapering of the normal temporal bone.